1. Field of the Invention
The present invention relates generally to suspension systems for wheel supported vehicles, and more particularly to suspension systems for vehicles such as man-carrying mobile work platforms (where it is desirable to maintain the plane of the work platform as level as possible for the safety and comfort of the passengers).
2. The Prior Art
Axle suspension systems for wheel supported vehicles may be categorized as being of either the solid or oscillating tape. Solid transverse axles are frequently employed since such axles are less complicated structurally, and generally less expensive to manufacture. When steering is required, typically, a power assist motor is added to assist the steering function.
The primary disadvantage of such configurations is that a solid axle suspension results in a rigid ride and the main frame of the vehicle is subject to tilt whenever rough terrain is traversed, making the work surface of the vehicle uncomfortable and unsafe to ride upon or work from. A second disadvantage is that, on uneven surfaces, the wheels can assume a non-perpendicular attitude with respect to ground due to the rigidity of their coupling, introducing stress into the wheel spindle and king pin connections and advancing the wear of these parts. Also, the center of gravity of mobile work platforms is relatively higher than that of other vehicles, which increases their instability or uneven surfaces.
Attempts have been made to overcome the above deficiencies by making axles of a two-piece, oscillating construction, pivotal at the center. Theoretically, whenever a depression or incline is encountered by one side of the vehicle, the wheel on that side will pivot about the center of the axle, but the position of the opposite wheel will not be affected. Also, the main frame on that side will either raise or lower, while the opposite side will not react.
While the oscillating, center pivot, axle is an improvement over the solid axle, certain attendant shortcomings prevent it from representing an ideal solution to the industry's needs. First, the full effect of an irregularity in the road surface is transferred and made manifest on one side of the work platform or main frame, resulting in undesirable listing. Further, the wheels are susceptible to skewing from a vertical position whenever uneven terrain is encountered, as in the solid axle configurations. Moreover, present suspension systems utilize a dual cylinder lockout to prevent a vehicle from shifting laterally or forward whenever the unit is in a work position. Such a lockout requires a more complicated hydraulic system comprising two lock out cylinders, (one at each suspension arm), a transfer rod, hosing, etc., which is relatively expensive.